Whereas pie graphs, frequency histograms, and frequency polygons are useful for plotting frequency data, a line graph is useful for plotting data generated by experiments. It uses lines to represent the relationship between independent variables and dependent variables. If you skim through your introductory psychology textbook, you will see several examples of line graphs. The graph shown in Figure 3 below represents the data from an experiment on exercise and weight loss. Note in this figure that one end of the line represents a group of people who agree to exercise regularly and the end of the line represents a group of people who do not engage in exercise. In all other ways these two groups are equal. They are weighed immediately after agreeing to participate in the study and again two weeks after agreeing to participate. A weight loss value is calculated for each participant and then the weight loss values for the participants in each group are averaged. Note that this graph allows the reader to note quickly the benefits of exercise on weight loss.